JP5454564B2 - Developing device and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a developing device that includes a regulating member that regulates the transport amount of a two-component developer composed of toner and a carrier to a development area, and an image forming apparatus including the developing device.

  The developing device as described above is provided with a toner replenishment mechanism because it is necessary to replenish the toner consumed by the development. This toner replenishing mechanism is often provided on one end side in the longitudinal direction of the developing roller provided in the developing device in order to save space. In this arrangement, it is necessary to circulate the replenished toner in the longitudinal direction of the developing roller. If the circulation speed is slow, supply cannot catch up with toner consumption, resulting in an image failure. Therefore, it is necessary to circulate the toner at a certain speed or higher.

  In view of the above-described background, some developing devices have a two-component developer stirred and circulated by, for example, a biaxial screw, and a developing roller is provided above one of the screws. . In this developing device, the two-component developer is supplied onto the outer peripheral surface of the developing roller by the magnetic force from the magnet body built in the developing roller.

  In the above configuration, since the liquid level of the two-component developer varies due to stirring and circulation, the amount of the two-component developer supplied to the developing roller varies. This variation may cause image defects. In order to reduce such image defects, first, a two-component developer is supplied onto the surface of the developing roller, and then the amount of the two-component developer on the developing roller is regulated by a regulating member provided in the developing device. Is adopted. However, since the developing roller must transport more than the necessary amount of the two-component developer to the regulating member, the driving torque of the developing roller is increased. Further, due to the stress applied to the two-component developer in the regulating member, the driving torque of the developing roller is increased or the two-component developer is deteriorated.

  Incidentally, as a conventional developing device, for example, there is one described in Patent Document 1 below. In order to stabilize the developer transport amount upstream of the regulating member (layer thickness regulating member), the developing device is provided with a slip regulating member disposed opposite to the developing roller on the upstream side of the regulating member. It has. The slip regulating member presses the two-component developer on the developing roller in a direction that prevents the two-component developer from sliding on the developing roller.

JP 2008-15197 A (FIG. 1)

  However, in the configuration of Patent Document 1, since the two-component developer is peeled off only at the upstream end portion of the slip regulating member, there is a possibility that an excessive two-component developer more than the necessary amount may be conveyed to the regulating member. is there. Further, according to this configuration, the stress is applied to the two-component developer at the upstream end.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a developing device that does not transport an extra two-component developer to a regulating member and that can further suppress stress on the two-component developer, and an image forming apparatus including the developing device. It is to be.

  In order to achieve the above object, one aspect of the present invention is a developing device that forms a toner image by developing an electrostatic latent image formed on an electrostatic image bearing member with a developer. A housing that is disposed opposite to the electrostatic image carrier and accommodates the developer, and rotates while carrying the developer supplied from the housing, and is transported to a development area that is opposite to the electrostatic image carrier. In the rotational direction of the carrier and the developer carrier, the developer carried on the developer carrier is disposed opposite to the developer carrier on the downstream side of the developer supply location in the housing with a gap. A guide member through which the agent passes through the space, the guide member spaced apart from the guide member on the downstream side in the rotation direction with respect to the guide member, and opposed to the developer carrier, with a gap therebetween, Between the developer carrier A regulating member that regulates the amount of developer that has passed through the gap, a catch pole that is fixedly incorporated in the developer carrier, and arranged as a plurality of magnetic poles from upstream to downstream in the rotation direction, And a magnet body having at least a pole and a regulation pole.

  The catch pole is disposed so as to be substantially opposed to the supply location, and the developer is adsorbed to the developer carrier from the supply location, and the transport pole is upstream of the rotation direction with respect to the regulation pole. It is adjacent and is arranged so as to face the guide member, the restricting pole is arranged so as to face the restricting member substantially, and the upstream end of the guide member has a magnetic flux density of the catch pole. The magnetic flux density of the transport pole is substantially lower than the peak position and downstream of the rotational direction and upstream of the rotational direction than the position where the magnetic flux density of the transport pole is substantially zero. The magnetic attraction force at the upstream end is smaller than the magnetic attraction force at the regulating member.

  Another aspect of the present invention is an image forming apparatus including the developing device.

  With the above-described configuration, it is possible to provide a developing device that does not transport excess two-component developer to the regulating member and can further suppress stress on the two-component developer, and an image forming apparatus including the developing device. Become.

1 is a schematic diagram illustrating an image forming apparatus to which a developing device according to an embodiment of the present invention can be applied. It is a longitudinal cross-sectional view which shows the typical structure of the developing device which concerns on this embodiment. It is a longitudinal cross-sectional view which shows an example of the position of the upstream edge part of FIG. 2A. It is a longitudinal cross-sectional view which shows the other example of the position of the upstream edge part of FIG. 2A. It is a longitudinal cross-sectional view which shows the magnetic attraction force of the principal part in the developing device of FIG. 2A. 5 is a longitudinal sectional view showing a schematic configuration of a developing device according to Comparative Example 1. FIG. 10 is a longitudinal sectional view showing a schematic configuration of a developing device according to Comparative Example 2. FIG. 10 is a longitudinal sectional view showing a schematic configuration of a developing device according to Comparative Example 3. FIG. 6 is a graph showing the stability of the amount of developer supplied to the developing roller with respect to liquid level fluctuations in the present embodiment and Comparative Examples 1 to 3. It is a graph which shows the rotational torque of the developing roller in this embodiment and Comparative Examples 1-3. It is a graph which shows deterioration of the developer D in this embodiment and Comparative Examples 1-3.

(Schematic configuration of image forming apparatus)
First, an image forming apparatus to which a developing device according to an embodiment of the present invention can be applied will be described. In FIG. 1, an image forming apparatus 10 is a printer that forms a monochrome image on a recording medium S such as recording paper.

  The image forming apparatus 10 includes a photosensitive drum 1 as a typical example of an electrostatic image carrier. In the image forming apparatus 10, around the photosensitive drum 1, a charger 2, an image exposure device 3, a developing device 4, a transfer roller 5, and a cleaning device 6 are arranged in this order. In addition, the image forming apparatus 10 includes a recording medium S supply unit, and a fixing device 7 and a discharge tray downstream of the transfer roller 5 along the conveyance direction of the recording medium S from the supply unit. In addition, about a supply part and a discharge tray, illustration is abbreviate | omitted for convenience.

  The photoreceptor drum 1 is, for example, a negatively chargeable photoreceptor, and the surface thereof is uniformly charged to a predetermined negative potential by the charger 2.

  The image exposure device 3 exposes the surface of the photosensitive drum 1 charged by the charger 2 based on input image information, thereby forming an electrostatic latent image on the surface. The image information is transmitted from an image reading device, a computer, an external facsimile, or the like (not shown).

  The developing device 4 develops the electrostatic latent image on the photosensitive drum 1 using a two-component developer (hereinafter simply referred to as “developer”) including toner and a magnetic carrier. Here, the toner is, for example, a negatively charged toner having an average particle diameter of 6 μm made by a polymerization method. The magnetic carrier has an average particle size of 33 μm. The developing device 4 develops the electrostatic latent image by reversal development using negatively charged toner to form a toner image. The detailed configuration of the developing device 4 will be described later.

  According to the image forming apparatus 10 having the above configuration, a toner image is formed on the recording medium S as follows. First, the photosensitive drum 1 is rotationally driven in a clockwise direction (hereinafter referred to as a rotational direction CW) indicated by an arrow CW in FIG. The surface of the photosensitive drum 1 is uniformly charged to a predetermined potential by a charger 2 to which a charging bias is applied. The image exposure device 3 exposes the charged area, whereby an electrostatic latent image based on the input image information is formed on the surface of the photosensitive drum 1. The developing device 4 develops the electrostatic latent image, whereby a toner image is formed on the photosensitive drum 1.

  Further, the recording medium S from the supply unit is supplied to the timing roller TR of FIG. The recording medium S is adjusted in timing by the timing roller TR, and is introduced into and passed through the transfer nip between the photosensitive drum 1 and the transfer roller 5. At this time, a transfer voltage from a transfer power source (not shown) is applied to the transfer roller 5, and the toner image on the photosensitive drum 1 is transferred onto the recording medium S. The recording medium S to which the toner image is transferred passes through the fixing device 7. In the fixing device 7, the recording medium S is heated and pressurized, whereby the toner image is fixed on the recording medium S and discharged onto the discharge tray. After the toner image is transferred, the surface of the photosensitive drum 1 is cleaned by the cleaning device 6 and is prepared for the next image formation.

(Configuration of this developing device)
Next, the developing device 4 of FIG. 1 will be described in detail with reference to FIGS. 2A to 9. In FIG. 2A, the developing device 4 includes a housing 40, a developing roller 41, a magnet body 42, and a regulating member 43.

  The developing roller 41 is a typical example of a developer carrier. The developing roller 41 is made of a nonmagnetic material, and is a cylindrical sleeve having an outer diameter of 16 mm, for example. The outer peripheral surface of the developing roller 41 has an appropriate roughness for conveying the developer D, for example, by blasting.

  The developing roller 41 faces the photosensitive drum 1 with a gap in the housing 40 that opens toward the photosensitive drum 1. In FIG. 2A, the photosensitive drum 1 is only partially drawn for the convenience of illustration. Further, the developing roller 41 is driven to rotate in the arrow direction CW about the rotation center line CL in FIG. 2A by a developing motor (not shown). Here, the direction perpendicular to the conveyance direction of the recording medium S (see FIG. 1) is defined as the width direction of the recording medium S. The developing roller 41 is formed long in the direction along the rotation center line CL so as to be compatible with the storage medium S having various sizes in the width direction.

  Here, the housing 40 is provided with conveying members 441 and 442 made of, for example, a pair of screw conveyors. The conveying members 441 and 442 are arranged in parallel with the rotation center line CL described above. These conveying members 441 and 442 receive the driving force from the developing motor described above via a transmission mechanism. With this driving force, the conveying members 441 and 442 are rotationally driven within the housing 40. Thereby, the developer D in the housing 40 is agitated. By this stirring, the toners rub against each other and become charged.

  Further, the developer D is transported in the housing 40 along the longitudinal direction of the developing roller 41 (the direction of the rotation center line CL) by the rotational driving of the transport members 441 and 442. Specifically, the developer D is transported from the front side to the back side in FIG. 2A by one transport member 441. Thereafter, the developer D moves from the opening (not shown) formed on the back side of the partition 400 provided between the two conveying members 441 and 442 to the other conveying member 442. By the transport member 442, the developer D is transported from the back side to the near side of the paper, and moves to the transport member 441 from an opening formed on the near side of the partition 400. Thus, the developer D is circulated and conveyed in the housing 40 while being agitated.

  The housing 40 is provided with a developer D supply portion facing the developing roller 41. The developer D is distributed almost evenly to the supply location of the housing 40 by the above-described circulation conveyance, and is supplied to the outer peripheral surface of the developing roller 41 from this supply location. Note that the replenishment of the developer D is performed, for example, from the back side of the conveying member 442.

  The magnet body 42 is built in the developing roller 41. For example, five magnet pieces are arranged in a roll shape in the circumferential direction. The magnet body 42 has a catch pole S1, a transport pole N1, a regulation pole S2, a development pole N2, and a separation pole S3 as magnetic poles. Note that “S” and “N” included in the reference symbols mean the S pole and the N pole.

  First, the catch pole S <b> 1 is provided so as to be generally opposed to the supply location of the housing 40, and the developer D in the housing 40 is adsorbed and supported on the outer peripheral surface of the developing roller 41 from the supply location.

  The conveyance pole N1 is disposed so as to face a guide passage 46 described later, as enlargedly illustrated on the left side in FIG. 2A. The transport pole N <b> 1 is a magnetic pole for transporting the developer D that passes through the guide passage 46 toward the regulating member 43.

  The regulation pole S2 and the development pole N2 are provided at positions facing the regulation member 43 and the development area Da. The separation pole S3 is provided between the development pole N2 and the catch pole S1, forms a repulsive magnetic field therebetween, and the magnetic flux density along the radial direction of the development roller 41 is, for example, a low magnetic force range of 5 mT or less. LM is formed. The magnetic flux density is originally defined by a vector quantity, but the magnetic flux density in the present application indicates the magnitude of the component in the radial direction of the developing roller 41 (the normal direction of the surface of the developing roller 41). .

Here, the peak magnetic flux density of each magnetic pole is as follows.
・ Catch pole S1: 40mT
・ Transport pole N1: 35 mT
・ Regulation electrode S2: 37mT
・ Development pole N2: 100 mT
Separation pole S3: 60 mT

  The restricting member 43 is made of a magnetic material, and is disposed on the upstream side of the developing area Da with respect to the rotation direction CW of the developing roller 41. Further, the regulating member 43 is arranged to face the developing roller 41 with a gap g1. 2A, it is preferable that a protrusion 431 is formed on the upstream end face of the restricting member 43 in the direction opposite to the rotational direction CW. The protrusion 431 has a length P in the direction opposite to the rotation direction CW.

  The developing device 4 further includes a guide member 45 disposed on the upstream side of the regulating member 43 along the rotation direction CW of the developing roller 41. The guide member 45 is made of a nonmagnetic material. The guide member 45 is a plate-like member whose cross-sectional shape is an arc shape along the rotation direction CW and has a thickness of approximately 3 mm.

  Such a guide member 45 is disposed between the developing roller 41 and the inner surface 401 of the housing 40, and the guide member 45 is disposed so as to have a gap g <b> 2 between the developing roller 41 and face the above-described transport pole N <b> 1. Is done. The gap g2 is used as a guide passage 46 that guides the developer D1 to the gap g1. Note that the surface of the guide member 45 that faces the developing roller 41 desirably has good lubricity, for example, by coating with a fluorine resin.

  Further, the guide member 45 is disposed with a gap g <b> 6 between the housing inner surface 401. The gap g6 is used as a reflux passage 47 that causes the developer D that has passed through the guide passage 46 to flow back toward the upstream end 451 of the guide member 45.

  Further, the downstream end of the guide member 45 along the rotational direction CW is spaced apart from the protrusion 431 of the regulating member 43 with a gap g5, thereby forming a communication passage 48 that communicates from the guide passage 46 to the reflux passage 47. Is done.

  Here, the gap g1 is 0.5 mm, the gap g2 is 1.5 mm, the gap g6 is 2.0 mm, the distance P is 3.0 mm, and g5 is 1.5 mm, for example. It is.

  Here, as shown in FIG. 2A and the like, the position of the upstream end 451 of the guide member 45 is first set downstream of the rotational direction CW with respect to the peak position of the magnetic flux density of the catch pole S1. In FIG. 2A, the magnetic flux density distribution is schematically shown by dotted lines. This also applies to FIGS. 2B and 2C.

  Further, as shown in FIG. 2B, the position of the upstream end 451 passes through a position where the magnetic flux density is approximately 0 mT between the catch pole S <b> 1 and the transport pole N <b> 1 and extends in the normal direction of the developing roller 41. Matches the line VLa. Or as shown to FIG. 2C, the upstream edge part 451 may be located in the upstream with respect to the rotation direction CW rather than the above-mentioned virtual line VLa.

  Further, here, as shown in FIG. 3, the magnetic attraction force Fa is the magnetic attraction force in the normal direction of the developing roller 41 at the position of the upstream end 451, and the magnetic attraction force Fb is the above-described regulating member. The magnetic attraction force in the normal direction of the developing roller 41 at the position of the gap g1 of 43 is defined as In FIG. 3, the distribution of the magnetic attractive force is schematically indicated by a one-dot chain line. In the present embodiment, the position of the upstream end 451 and the magnet body 42 are designed so that the magnetic attractive force Fa is smaller than the magnetic attractive force Fb. For example, the magnetic attractive force Fa is 1.40 g at a distance of 0.1 mm from the surface of the developing roller 41, and the magnetic attractive force Fb is 2.01 g under the same conditions. The magnetic attractive forces Fa and Fb can be measured using a load cell for scales.

(Conveying developer in this developing device)
Next, the transport path of the developer D will be briefly described. In FIG. 2A, the developer D adsorbed on the surface of the developing roller 41 by the magnetic force of the catch pole S1 of the magnet body 42 is caused by the rotation of the developing roller 41 to cause a gap between the regulating members 43 under the action of frictional force from the catch pole S1. It is transported toward g1. The developer D carried on the surface of the developing roller 41 first reaches the upstream end 451 of the guide member 45. The upstream end 451 limits the amount of developer D transported so as not to be excessive.

  Further, a guide passage 46 and a reflux passage 47 are formed by the guide member 45 as a path of the developer D immediately upstream of the regulating member 43. In the guide passage 46, the developer D that has passed through the upstream end 451 is conveyed in the same direction as the rotation direction CW of the developing roller 41. Part of the developer D that has passed through the guide passage 46 passes through the gap g1 of the regulating member 43 and is supplied to the development area Da on the downstream side thereof.

  On the other hand, the developer D regulated by the regulating member 43 flows from the guide passage 46 into the reflux passage 47 through the communication passage 48. The developer D that has flowed in moves toward the upstream end 451 of the guide member 45 according to gravity.

(Operation and effect of the developing device of this embodiment)
What is characteristic of the developing device 4 is that (1) the position of the upstream end 451 is downstream of the peak position of the magnetic flux density of the catch pole S1 (see FIG. 2A). ) The position of the upstream end 451 is adjusted to the position where the magnetic flux density is 0 mT between the catch pole S1 and the transport pole N1 (see FIG. 2B), or upstream of the position where the magnetic flux density is 0 mT. Yes (see FIG. 2C), (3) The magnetic attractive force Fa at the upstream end 451 is smaller than the magnetic attractive force Fb at the gap g1 of the regulating member 43 (see FIG. 3). As a result, it is possible to suppress the stress on the two-component developer further without conveying an extra two-component developer. In order to clarify such a technical effect, the inventor of the present application compared the developing device 4 with the developing devices of Comparative Examples 1 to 3 shown in FIGS.

  First, as shown in FIG. 4, the comparative example 1 is different from the developing device 4 only in that the position of the upstream end 451a of the guide member 45 is not on the downstream side of the peak position of the magnetic flux density of the catch pole S1. Compared and different.

  Further, as shown in FIG. 5, in Comparative Example 2, the position of the upstream end 451b of the guide member 45 is provided on the downstream side of the position of 0 mT between the catch pole S1 and the transport pole N1. Only in this respect, it differs from the developing device 4.

  Further, as shown in FIG. 6, the comparative example 3 is developed only in that the magnetic attractive force Fa at the upstream end 451c of the guide member 45 is not smaller than the magnetic attractive force Fb in the gap g1 of the regulating member 43. It differs from the device 4.

  In the comparative example 1 of FIG. 4, the upstream end 451a of the guide member 45 is provided on the upstream side of the peak position of the magnetic flux density of the catch pole S1. Therefore, the supply amount of the developer D to the guide passage 46 of the guide member 45 is limited by the arrangement of the catch pole S1. Therefore, although it is possible to prevent the excessive developer D from being transported, as can be seen by referring to the curve plotted in (2) in FIG. 7, the liquid level of the developer D due to the stirring of the transport members 441 and 442 is prevented. Thus, it was confirmed that the stability of the supply amount of the developer D to the developing roller 41 was lowered.

  Further, in Comparative Example 2 in FIG. 5, similarly to the developing device 4, the upstream end 451 b of the guide member 45 is provided downstream of the peak position of the magnetic flux density of the catch pole S <b> 1. Therefore, the comparative example 2 has the stability of the supply amount of the developer D to the developing roller 41 substantially equal to that of the developing device 4 as can be seen by referring to the curve plotted with ▲ in FIG. However, in Comparative Example 2, the upstream end portion of the guide member 45 is provided on the downstream side of the 0 mT position between the catch pole S1 and the transport pole N1. Therefore, since the distance from the catch pole S1 to the upstream end of the guide member 45 is increased, the amount of extra developer D transported is increased. As a result, as can be seen with reference to FIG. 8, it was confirmed that in Comparative Example 2, the rotational torque of the developing roller 41 increased as compared with the developing device 4.

  Further, in Comparative Example 3 in FIG. 6, similarly to the developing device 4, the upstream end 451 c of the guide member 45 is provided on the downstream side of the peak position of the magnetic flux density of the catch pole S <b> 1. Therefore, Comparative Example 3 has the developer supply amount stability to the developing roller 41 substantially equal to that of the developing device 4, as can be seen by referring to the curve plotted with x in FIG. However, in Comparative Example 3, the magnetic attractive force Fa at the upstream end is larger than the magnetic attractive force Fb in the gap g1 of the regulating member 43. Therefore, at the upstream end portion 451c of the guide member 45, the developer is peeled off from the developing roller 41 against the relatively strong magnetic attraction when the transport amount of the developer is regulated. Here, FIG. 9 is a graph in which the charge amount of the developer with respect to the number of recording media S on which an image is formed is measured for each of the present embodiment and Comparative Examples 1 to 3. As can be seen from FIG. 9, regarding Comparative Example 3, as the number of sheets increases, the charge amount of the developer decreases. Thus, with respect to Comparative Example 3, it was confirmed that a strong stress was given to the developer, and as a result, the developer was likely to be deteriorated quickly.

  On the other hand, the developing device 4 has the above-described features (1) to (3), which makes it possible to suppress the distance for transporting excess developer. It is possible to suppress an increase in the rotational torque of 41. Further, according to the feature (3), the developing device 4 does not require excessive energy when the developer is peeled off from the developing roller 41 at the upstream end 451 of the guide member 45. Therefore, in the present developing device 4, it is possible to suppress the deterioration of the developer without applying a strong stress to the developer.

(Appendix)
In the above embodiment, the image forming apparatus 10 has been described as forming a monochrome image. However, the present invention is not limited thereto, and the developing device 4 may be employed in an image forming apparatus that forms a color image. In this case, the image forming apparatus is provided with developing devices for four colors, for example, yellow, magenta, cyan, and black. At least one of these developing devices has been described in this embodiment. If it is okay.

  Further, since the image forming apparatus 10 includes the developing device 4, the stress of the developer is suppressed, and thus the deterioration of the developer is reduced. Accordingly, it is possible to provide the image forming apparatus 10 that can suppress the occurrence of image defects and the like and can form a good image.

  Moreover, although the above embodiment demonstrated that the single conveyance pole N1 was provided, not only this but the some conveyance pole N1 arrange | positioned so as to oppose the guide channel | path 46 may be provided. Absent. In this case, the upstream end 451 of the guide member 45 is located at a position where the magnetic flux density of the plurality of transport poles N1 adjacent to the regulation pole S2 on the upstream side in the rotational direction CW is substantially zero. Is also provided upstream of the rotational direction or at a position where the magnetic flux density of the carrier pole is substantially zero.

  When a plurality of transport poles are provided, all the transport poles do not have to be the same, and may be configured to include both the N pole and the S pole.

  The fixing device according to the present invention does not convey an extra two-component developer, and can further suppress the stress on the two-component developer. In addition to a monochrome printer and a tandem type electrophotographic printer, a copying machine, a facsimile It can be applied to these multifunction devices.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 1 Photosensitive drum (electrostatic image carrier)
4 Developing Device 40 Housing 41 Developing Roller (Developer Carrier)
42 Magnet body S1 Catch pole N1 Transport pole S2 Restriction pole 43 Restriction member 45 Guide member 451 Upstream end 46 Guide passage 47 Recirculation passage

Claims (3)

A developing device for developing a latent electrostatic image formed on an electrostatic image carrier with a developer to form a toner image,
A housing containing the developer;
A developer carrying body disposed opposite to the electrostatic image carrying body, rotating while carrying the developer supplied from the housing, and transported to a development area which is a place facing the electrostatic image carrying body;
In the rotational direction of the developer carrier, the developer carrier is disposed opposite to the developer carrier at a downstream side of the developer supply location in the housing, and the developer carried on the developer carrier is disposed in the gap. A guide member passing through,
The guide member is spaced downstream from the guide member along the rotation direction, and is opposed to the developer carrier with a gap therebetween. A gap between the guide member and the developer carrier is provided. A regulating member that regulates the amount of developer that has passed;
A magnetic body that is fixedly incorporated in the developer carrying member and has at least a catch pole, a transport pole, and a regulation pole arranged as a plurality of magnetic poles from upstream to downstream in the rotation direction,
The catch pole is disposed so as to be generally opposed to the supply location, and adsorbs the developer from the supply location to the developer carrier,
The transport pole is adjacent to the regulation pole on the upstream side with respect to the rotation direction, and is disposed to face the guide member,
The restriction electrode is disposed so as to be generally opposed to the restriction member,
The upstream end portion of the guide member is located downstream of the rotation direction from the position where the magnetic flux density of the catch pole reaches a peak, and from the position where the magnetic flux density of the transport pole is substantially zero. Upstream of the rotational direction, or at a position where the magnetic flux density of the carrier pole is substantially zero,
The developing device, wherein a magnetic attraction force at the upstream end is smaller than a magnetic attraction force at the regulating member. The gap between the guide member and the developer carrier is used as a guide passage through which the developer carried on the developer carrier passes.
The guide member further forms a return passage by a gap between the guide member and the inner surface of the housing,
2. The return path is connected to the guide path via a communication path, and returns the developer regulated by the regulation member to the upstream end portion of the guide member with respect to the rotation direction. Development device.   An image forming apparatus comprising the developing device according to claim 1.

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